In most current color picture tube types, a peripheral frame supporting a shadow mask is suspended in a faceplate panel by means of springs that are welded either directly to the frame or to plates which in turn are welded to the frame. In the directly welded version, the springs are usually made of bimetallic materials; and in the plate version, the plates are bimetallic. As the springs or plates become heated by transfer of heat from the mask through the frame, the bimetallic materials expand differently, thereby bending the springs or plates to cause movement of the mask-frame assembly toward a screen disposed on the panel.
It is common to use either three or four springs to support a mask-frame assembly within a rectangular faceplate panel of a tube. In a three-spring support system, one spring is usually located at the upper center of the mask, and the other two springs are located along the sides of the tube between the centers of the sides of the mask and the lower two corners of the mask. In a four-spring support system, springs are usually located at the top and bottom centers of the mask and at the left and right centers of the mask. In both the three- and four-spring support systems, as described above, it is possible for the mask-frame assembly to twist slightly and shift relative to the faceplate, during tube manufacture and/or operation.
A known means for minimizing twisting and shifting of a mask-frame assembly uses spring supports at the four corners of the frame. Embodiments for achieving such corner support are shown in U.S. Pat. No. 4,723,088, issued to Sone et al. on Feb. 2, 1988, and in U.S. Pat. No. 4,728,853, issued to Sone et al. on Mar. 1, 1988.
A problem encountered using corner mask supports in a tube having a 16.times.9 aspect ratio is that there is insufficient room for the mask supports in the corners to permit proper insertion and removal of the mask. This problem occurs because of the decreased angle (29.36.degree.) the tube diagonal makes with the tube major axis in a 16.times.9 aspect ratio tube, as compared to the corresponding angle (36.87.degree.) in a 4.times.3 aspect ratio tube. When the corners of a mask frame are angled perpendicularly to the diagonal in a 16.times.9 aspect ratio tube, the clearance between the mask support and the long side of the tube faceplate becomes very small. Therefore, it is desirable to modify the mask support means to provide additional clearance in a tube, preferably a 16.times.9 aspect ratio tube, between the mask support and the long side of a tube faceplate panel skirt.